Hello, Is the phenomenon of wellbore storage depends on fluid type of reservoir? How does it effect well-test design?
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Farooq Mohibuddin
Jun 23, 2017
Hello Rohit,
Thank you for interacting at ProPetra. Wellbore storage is common in most welltest. As the word implies, wellbore storage is the period after well is shut-in to record build-up/fall-off data when fluid from reservoir keeps flowing into the wellbore. As all fluids are compressible to varying extent, when well is shutin from surface, this doesnot mean flow from the reservoir ceases instantenously. Until reservoir flows into the wellbore, the pressure data recorded over that time is called wellbore storage and has a characteristic shape on the Bourdet Derivative Log-Log plot.
Now, as gas is considerably more compressible than liquid, when reservoir is flowing into the wellbore gas keeps compressing and allows more fluid to be flowed. This generally means that wellbore storage time for gas producing wells is relatively higher than for wells with minimum gas production.
For a reservoir that produces dry gas through a 10,000ft deep well, and that too in minute rates (such as 0.5 million cubic feet per day), wellbore storage times may be very long if well is shut-in from surface. Often data recorded for 24hrs or more may not show any reservoir properties as most data is in wellbore storage period.
A quick remedy to counter wellbore storage is downhole shut-in. By decreasing the amount of volume available after shut-in, we decrease the wellbore storage time significantly saving shut-down costs and minimizing lost revenue due to lost production.
Hello Rohit,
Thank you for interacting at ProPetra. Wellbore storage is common in most welltest. As the word implies, wellbore storage is the period after well is shut-in to record build-up/fall-off data when fluid from reservoir keeps flowing into the wellbore. As all fluids are compressible to varying extent, when well is shutin from surface, this doesnot mean flow from the reservoir ceases instantenously. Until reservoir flows into the wellbore, the pressure data recorded over that time is called wellbore storage and has a characteristic shape on the Bourdet Derivative Log-Log plot.
Now, as gas is considerably more compressible than liquid, when reservoir is flowing into the wellbore gas keeps compressing and allows more fluid to be flowed. This generally means that wellbore storage time for gas producing wells is relatively higher than for wells with minimum gas production.
For a reservoir that produces dry gas through a 10,000ft deep well, and that too in minute rates (such as 0.5 million cubic feet per day), wellbore storage times may be very long if well is shut-in from surface. Often data recorded for 24hrs or more may not show any reservoir properties as most data is in wellbore storage period.
A quick remedy to counter wellbore storage is downhole shut-in. By decreasing the amount of volume available after shut-in, we decrease the wellbore storage time significantly saving shut-down costs and minimizing lost revenue due to lost production.
Hope this helps.
Farooq